T— Continued 



turbidity— A condition where transparency turnover— (1) in production, the rate at 

 of water is reduced. It is an optical which something is used up and re- 

 phenomenon and does not necessarily placed. (2) In a limnological sense, the 

 have a direct linear relationship to partic- mixing of layers of lentic waters and the 

 iilate concentration. redistribution of oxygen and nutrients. 



--U-- 



ultraplankton— Organisms smaller than 5 

 micrometers in size. 



__ v-- 



vagility— The innate ability of an organism 

 to move. Locomotion, dispersion, etc. 



vitality— Reproductive success. 



viviporous— A type of reproduction where 

 the offspring are born alive. They 

 develop within the mother's body and 

 derive nourishment directly from her. 

 Compare with oviparous and ovovivi- 

 parous. 



--X-- 



xeric— A prefix meaning dry. 



xerophyte— A plant with very low water 

 requirements as opposed to hydrophyte. 



--Z-- 



zoocoenosis— The animal community as 

 opposed to phytocoenosis, the plant 

 community. See also biocoenosis. 



zooneuston— Animals found on the surface 

 film of water. 



zooplankton— Animals in the plankton. 



18 



